THREE-DIMENSIONAL HUCKEL MOLECULAR ORBITAL ENERGY LEVEL CORRELATION DIAGRAMS FOR POLYHEDRAL REARRANGEMENTS

摘要

A three-dimensional Huckel method recently developed for cluster compounds has been used to investigate polyhedral rearrangements of organic molecules as well as main-group inorganic clusters. The method starts from information about atomic connectivity and number of cluster electrons, familiar and convenient concepts for chemists. Calculations lead to diagrams that show how molecular orbital (MO) energy levels and second moment scaled total energies correlate between different structural forms. We consider diamond-square-diamond (DSD) framework reorganization mechanisms for pseudo-rotations of the closo-boranes. For B5H52- and B9H92-, is not allowed by the principle of conservation of orbital symmetry. DSD rearrangements are allowed for the other closo-boranes we studied here, with increasing activation energies, B8H82- similar to B11H112- similar to B10H102- < B6H62-, depending on the number of square faces opened during rearrangement. MO correlation diagrams and corresponding total energy curves for various numbers of cluster electrons provide visual rationalizations of observed structural trends with different numbers of cluster electrons. In particular? we discuss framework reorganizations for square to tetrahedron, hexagon to trigonal prism, hexagon to octahedron and cube to square antiprism. [References: 67]